1. Field of the Invention
The present invention relates generally to the field of radiation curable ink compositions, and more particularly to radiation curable ink compositions and vehicles therefor which contain water insoluble components and which can be printed in a substantially water insoluble form, but which can be cleaned up using aqueous solutions. The ink compositions of the present invention are substantially water insoluble when printed and water soluble or washable at certain selected alkaline pH levels when clean up is desired. The present invention also relates to a method of making and using such compositions.
2. Summary of the Prior Art
A wide variety of radiation curable inks currently exist in the art. In general, radiation curable inks and ink compositions dry or cure via free radical polymerization. The two most common radiation curing methods involve ultraviolet (UV) curing and electron beam (EB) curing, although other forms of radiation such as that derived from infra red and microwave energies are also commonly included in the category of radiation drying or curing and are thus included for purposes of defining the present invention.
A principal advantage of radiation curing involves the reduction of volatile organic compounds (VOCs) which have become the focus of many state and federal regulations. Many conventional inks dry by evaporation or other processes which involve the use of solvents and the evaporation of solvents during the drying or curing process. This necessarily results in the introduction of such solvents or VOCs into the atmosphere or creates disposal problems with respect to such solvents. The free radical polymerization of inks via UV or EB curing substantially reduces if not eliminates solvent emission concerns during the drying or curing process. A further advantage of radiation curable ink systems is that the inks are dried or cured only upon exposure to a particular actinic radiation or other free radical source. Thus, the premature drying of radiation curable inks in the ink containers or on printing plates and other application equipment can be avoided.
However, despite the recognized advantages of radiation curable inks over ink compositions which dry by solvent evaporation, certain limitations continue to exist. For example, although radiation curable inks can be formulated with little if any solvent component, the components of conventional radiation curable ink compositions are not water soluble to the extent that they can be washed or cleaned up with aqueous solutions. Thus, the cleanup of radiation curable inks from printing plates, rollers, brushes, blankets and other application equipment necessarily involves the use of nonaqueous, organic or other solvents which are capable of dissolving or washing, and thus cleaning up, the various resins and other components of the ink composition. In many cases, these solvents are volatile organic compounds or glycol ethers or esters. Some of these are considered as hazardous wastes, thereby creating obvious safety concerns and disposal problems. Others, even though not technically considered as hazardous wastes, still pose serious health and safety concerns. Various attempts have been made to overcome this problem by formulating water soluble radiation curable inks which are substantially water soluble and can thus be cleaned up with aqueous solutions. However, such water based or water soluble inks generally exhibit properties inferior to certain desired properties of water insoluble inks.
Accordingly, there is a need in the art for a radiation curable ink composition, and methods associated therewith, which has all of the advantageous characteristics of a water insoluble ink, including high resistance to water and alkali environments, but which can be washed and cleaned up using aqueous solutions.